The Mask — Patricia Bernard

Fourteen-year-old Rob Vian is in Venice to study architecture, enjoy Carnevale, and learn Italian. He also wants to track down his mother's ancestral palazzo, but no sooner does he arrive than he's attacked in the street by someone dressed as the Spirit of Death!
When the same thing happens again the next day, Rob and his cousin are determined to find out the truth. Who is the Spirit of Death? And why in the world does he keep attacking Rob?